/*
 * Circular Byte Buffer Copyright (C) 2002 Stephen Ostermiller
 * http://ostermiller.org/contact.pl?regarding=Java+Utilities This program is free software; you can redistribute it
 * and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation;
 * either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that
 * it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
 * PARTICULAR PURPOSE. See the GNU General Public License for more details. See COPYING.TXT for details.
 */
package eiisan.util.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * 环形输入输出缓冲<br>
 * 常用方式:<br>
 *
 * <pre>
 * // Create the buffer.
 * CircularByteBuffer buffer = new CircularByteBuffer();
 *
 * // Fill the buffer.
 * buffer.getOutputStream().write(
 *     new byte[]{
 *         'H','e','l','l','o',' ',
 *         'W','o','r','l','d','!','\n'
 *     }
 * };
 * buffer.getOutputStream().close();
 *
 * // Empty the buffer.
 * int c;
 * while ((c = buffer.getInputStream().read()) != -1){
 *     System.out.print((char)c);
 * }
 * </pre>
 *
 * Implements the Circular Buffer producer/consumer model for bytes. More information about this class is available from
 * <a target="_top" href= "http://ostermiller.org/utils/CircularByteBuffer.html">ostermiller.org</a>.
 * <p>
 * Using this class is a simpler alternative to using a PipedInputStream and a PipedOutputStream. PipedInputStreams and
 * PipedOutputStreams don't support the mark operation, don't allow you to control buffer sizes that they use, and have
 * a more complicated API that requires instantiating two classes and connecting them.
 * <p>
 * This class is thread safe.
 * @see CircularCharBuffer
 * @see CircularObjectBuffer
 * @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
 * @since ostermillerutils 1.00.00
 */
public class CircularByteBuffer {

	/**
	 * The default size for a circular byte buffer.
	 * @since ostermillerutils 1.00.00
	 */
	private final static int DEFAULT_SIZE = 1024;

	/**
	 * A buffer that will grow as things are added.
	 * @since ostermillerutils 1.00.00
	 */
	public final static int INFINITE_SIZE = -1;

	/**
	 * The circular buffer.
	 * <p>
	 * The actual capacity of the buffer is one less than the actual length of the buffer so that an empty and a full
	 * buffer can be distinguished. An empty buffer will have the markPostion and the writePosition equal to each other.
	 * A full buffer will have the writePosition one less than the markPostion.
	 * <p>
	 * There are three important indexes into the buffer: The readPosition, the writePosition, and the markPosition. If
	 * the InputStream has never been marked, the readPosition and the markPosition should always be the same. The bytes
	 * available to be read go from the readPosition to the writePosition, wrapping around the end of the buffer. The
	 * space available for writing goes from the write position to one less than the markPosition, wrapping around the
	 * end of the buffer. The bytes that have been saved to support a reset() of the InputStream go from markPosition to
	 * readPosition, wrapping around the end of the buffer.
	 * @since ostermillerutils 1.00.00
	 */
	protected byte[] buffer;

	/**
	 * Index of the first byte available to be read.
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int readPosition = 0;

	/**
	 * Index of the first byte available to be written.
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int writePosition = 0;

	/**
	 * Index of the first saved byte. (To support stream marking.)
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int markPosition = 0;

	/**
	 * Number of bytes that have to be saved to support mark() and reset() on the InputStream.
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int markSize = 0;

	/**
	 * If this buffer is infinite (should resize itself when full)
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile boolean infinite = false;

	/**
	 * True if a write to a full buffer should block until the buffer has room, false if the write method should throw
	 * an IOException
	 * @since ostermillerutils 1.00.00
	 */
	protected boolean blockingWrite = true;

	/**
	 * The InputStream that can empty this buffer.
	 * @since ostermillerutils 1.00.00
	 */
	protected InputStream in = new CircularByteBufferInputStream();

	/**
	 * true if the close() method has been called on the InputStream
	 * @since ostermillerutils 1.00.00
	 */
	protected boolean inputStreamClosed = false;

	/**
	 * The OutputStream that can fill this buffer.
	 * @since ostermillerutils 1.00.00
	 */
	protected OutputStream out = new CircularByteBufferOutputStream();

	/**
	 * true if the close() method has been called on the OutputStream
	 * @since ostermillerutils 1.00.00
	 */
	protected boolean outputStreamClosed = false;

	/**
	 * Make this buffer ready for reuse. The contents of the buffer will be cleared and the streams associated with this
	 * buffer will be reopened if they had been closed.
	 * @since ostermillerutils 1.00.00
	 */
	public void clear() {
		synchronized (this) {
			readPosition = 0;
			writePosition = 0;
			markPosition = 0;
			outputStreamClosed = false;
			inputStreamClosed = false;
		}
	}

	/**
	 * Retrieve a OutputStream that can be used to fill this buffer.
	 * <p>
	 * Write methods may throw a BufferOverflowException if the buffer is not large enough. A large enough buffer size
	 * must be chosen so that this does not happen or the caller must be prepared to catch the exception and try again
	 * once part of the buffer has been consumed.
	 * @return the producer for this buffer.
	 * @since ostermillerutils 1.00.00
	 */
	public OutputStream getOutputStream() {
		return out;
	}

	/**
	 * Retrieve a InputStream that can be used to empty this buffer.
	 * <p>
	 * This InputStream supports marks at the expense of the buffer size.
	 * @return the consumer for this buffer.
	 * @since ostermillerutils 1.00.00
	 */
	public InputStream getInputStream() {
		return in;
	}

	/**
	 * Get number of bytes that are available to be read.
	 * <p>
	 * Note that the number of bytes available plus the number of bytes free may not add up to the capacity of this
	 * buffer, as the buffer may reserve some space for other purposes.
	 * @return the size in bytes of this buffer
	 * @since ostermillerutils 1.00.00
	 */
	public int getAvailable() {
		synchronized (this) {
			return available();
		}
	}

	/**
	 * Get the number of bytes this buffer has free for writing.
	 * <p>
	 * Note that the number of bytes available plus the number of bytes free may not add up to the capacity of this
	 * buffer, as the buffer may reserve some space for other purposes.
	 * @return the available space in bytes of this buffer
	 * @since ostermillerutils 1.00.00
	 */
	public int getSpaceLeft() {
		synchronized (this) {
			return spaceLeft();
		}
	}

	/**
	 * Get the capacity of this buffer.
	 * <p>
	 * Note that the number of bytes available plus the number of bytes free may not add up to the capacity of this
	 * buffer, as the buffer may reserve some space for other purposes.
	 * @return the size in bytes of this buffer
	 * @since ostermillerutils 1.00.00
	 */
	public int getSize() {
		synchronized (this) {
			return buffer.length;
		}
	}

	/**
	 * double the size of the buffer
	 * @since ostermillerutils 1.00.00
	 */
	private void resize() {
		byte[] newBuffer = new byte[buffer.length * 2];
		int marked = marked();
		int available = available();
		if (markPosition <= writePosition) {
			// any space between the mark and
			// the first write needs to be saved.
			// In this case it is all in one piece.
			int length = writePosition - markPosition;
			System.arraycopy(buffer, markPosition, newBuffer, 0, length);
		} else {
			int length1 = buffer.length - markPosition;
			System.arraycopy(buffer, markPosition, newBuffer, 0, length1);
			int length2 = writePosition;
			System.arraycopy(buffer, 0, newBuffer, length1, length2);
		}
		buffer = newBuffer;
		markPosition = 0;
		readPosition = marked;
		writePosition = marked + available;
	}

	/**
	 * Space available in the buffer which can be written.
	 * @since ostermillerutils 1.00.00
	 */
	private int spaceLeft() {
		if (writePosition < markPosition) {
			// any space between the first write and
			// the mark except one byte is available.
			// In this case it is all in one piece.
			return markPosition - writePosition - 1;
		}
		// space at the beginning and end.
		return buffer.length - 1 - (writePosition - markPosition);
	}

	/**
	 * Bytes available for reading.
	 * @since ostermillerutils 1.00.00
	 */
	private int available() {
		if (readPosition <= writePosition) {
			// any space between the first read and
			// the first write is available.  In this case i
			// is all in one piece.
			return writePosition - readPosition;
		}
		// space at the beginning and end.
		return buffer.length - (readPosition - writePosition);
	}

	/**
	 * Bytes saved for supporting marks.
	 * @since ostermillerutils 1.00.00
	 */
	private int marked() {
		if (markPosition <= readPosition) {
			// any space between the markPosition and
			// the first write is marked.  In this case i
			// is all in one piece.
			return readPosition - markPosition;
		}
		// space at the beginning and end.
		return buffer.length - (markPosition - readPosition);
	}

	/**
	 * If we have passed the markSize reset the mark so that the space can be used.
	 * @since ostermillerutils 1.00.00
	 */
	private void ensureMark() {
		if (marked() >= markSize) {
			markPosition = readPosition;
			markSize = 0;
		}
	}

	/**
	 * Create a new buffer with a default capacity. Writing to a full buffer will block until space is available rather
	 * than throw an exception.
	 * @since ostermillerutils 1.00.00
	 */
	public CircularByteBuffer() {
		this(DEFAULT_SIZE, true);
	}

	/**
	 * Create a new buffer with given capacity. Writing to a full buffer will block until space is available rather than
	 * throw an exception.
	 * <p>
	 * Note that the buffer may reserve some bytes for special purposes and capacity number of bytes may not be able to
	 * be written to the buffer.
	 * <p>
	 * Note that if the buffer is of INFINITE_SIZE it will neither block or throw exceptions, but rather grow without
	 * bound.
	 * @param size desired capacity of the buffer in bytes or CircularByteBuffer.INFINITE_SIZE.
	 * @since ostermillerutils 1.00.00
	 */
	public CircularByteBuffer(int size) {
		this(size, true);
	}

	/**
	 * Create a new buffer with a default capacity and given blocking behavior.
	 * @param blockingWrite true writing to a full buffer should block until space is available, false if an exception
	 *        should be thrown instead.
	 * @since ostermillerutils 1.00.00
	 */
	public CircularByteBuffer(boolean blockingWrite) {
		this(DEFAULT_SIZE, blockingWrite);
	}

	/**
	 * Create a new buffer with the given capacity and blocking behavior.
	 * <p>
	 * Note that the buffer may reserve some bytes for special purposes and capacity number of bytes may not be able to
	 * be written to the buffer.
	 * <p>
	 * Note that if the buffer is of INFINITE_SIZE it will neither block or throw exceptions, but rather grow without
	 * bound.
	 * @param size desired capacity of the buffer in bytes or CircularByteBuffer.INFINITE_SIZE.
	 * @param blockingWrite true writing to a full buffer should block until space is available, false if an exception
	 *        should be thrown instead.
	 * @since ostermillerutils 1.00.00
	 */
	public CircularByteBuffer(int size, boolean blockingWrite) {
		if (size == INFINITE_SIZE) {
			buffer = new byte[DEFAULT_SIZE];
			infinite = true;
		} else {
			buffer = new byte[size];
			infinite = false;
		}
		this.blockingWrite = blockingWrite;
	}

	/**
	 * Class for reading from a circular byte buffer.
	 * @since ostermillerutils 1.00.00
	 */
	protected class CircularByteBufferInputStream extends InputStream {

		/**
		 * Returns the number of bytes that can be read (or skipped over) from this input stream without blocking by the
		 * next caller of a method for this input stream. The next caller might be the same thread or or another thread.
		 * @return the number of bytes that can be read from this input stream without blocking.
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public int available() throws IOException {
			synchronized (CircularByteBuffer.this) {
				if (inputStreamClosed) {
					throw new IOException("InputStream has been closed, it is not ready.");
				}
				return CircularByteBuffer.this.available();
			}
		}

		/**
		 * Close the stream. Once a stream has been closed, further read(), available(), mark(), or reset() invocations
		 * will throw an IOException. Closing a previously-closed stream, however, has no effect.
		 * @throws IOException never.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void close() throws IOException {
			synchronized (CircularByteBuffer.this) {
				inputStreamClosed = true;
			}
		}

		/**
		 * Mark the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to
		 * this point.
		 * <p>
		 * The readAheadLimit must be less than the size of circular buffer, otherwise this method has no effect.
		 * @param readAheadLimit Limit on the number of bytes that may be read while still preserving the mark. After
		 *        reading this many bytes, attempting to reset the stream will fail.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void mark(int readAheadLimit) {
			synchronized (CircularByteBuffer.this) {
				//if (inputStreamClosed) throw new IOException("InputStream has been closed; cannot mark a closed InputStream.");
				if (buffer.length - 1 > readAheadLimit) {
					markSize = readAheadLimit;
					markPosition = readPosition;
				}
			}
		}

		/**
		 * Tell whether this stream supports the mark() operation.
		 * @return true, mark is supported.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public boolean markSupported() {
			return true;
		}

		/**
		 * Read a single byte. This method will block until a byte is available, an I/O error occurs, or the end of the
		 * stream is reached.
		 * @return The byte read, as an integer in the range 0 to 255 (0x00-0xff), or -1 if the end of the stream has
		 *         been reached
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public int read() throws IOException {
			while (true) {
				synchronized (CircularByteBuffer.this) {
					if (inputStreamClosed) {
						throw new IOException("InputStream has been closed; cannot read from a closed InputStream.");
					}
					int available = CircularByteBuffer.this.available();
					if (available > 0) {
						int result = buffer[readPosition] & 0xff;
						++readPosition;
						if (readPosition == buffer.length) {
							readPosition = 0;
						}
						ensureMark();
						return result;
					} else if (outputStreamClosed) {
						return -1;
					}
				}
				try {
					Thread.sleep(100);
				} catch (Exception x) {
					throw new IOException("Blocking read operation interrupted.");
				}
			}
		}

		/**
		 * Read bytes into an array. This method will block until some input is available, an I/O error occurs, or the
		 * end of the stream is reached.
		 * @param cbuf Destination buffer.
		 * @return The number of bytes read, or -1 if the end of the stream has been reached
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public int read(byte[] cbuf) throws IOException {
			return read(cbuf, 0, cbuf.length);
		}

		/**
		 * Read bytes into a portion of an array. This method will block until some input is available, an I/O error
		 * occurs, or the end of the stream is reached.
		 * @param cbuf Destination buffer.
		 * @param off Offset at which to start storing bytes.
		 * @param len Maximum number of bytes to read.
		 * @return The number of bytes read, or -1 if the end of the stream has been reached
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public int read(byte[] cbuf, int off, int len) throws IOException {
			while (true) {
				synchronized (CircularByteBuffer.this) {
					if (inputStreamClosed) {
						throw new IOException("InputStream has been closed; cannot read from a closed InputStream.");
					}
					int available = CircularByteBuffer.this.available();
					if (available > 0) {
						int length = Math.min(len, available);
						int firstLen = Math.min(length, buffer.length - readPosition);
						int secondLen = length - firstLen;
						System.arraycopy(buffer, readPosition, cbuf, off, firstLen);
						if (secondLen > 0) {
							System.arraycopy(buffer, 0, cbuf, off + firstLen, secondLen);
							readPosition = secondLen;
						} else {
							readPosition += length;
						}
						if (readPosition == buffer.length) {
							readPosition = 0;
						}
						ensureMark();
						return length;
					} else if (outputStreamClosed) {
						return -1;
					}
				}
				try {
					Thread.sleep(100);
				} catch (Exception x) {
					throw new IOException("Blocking read operation interrupted.");
				}
			}
		}

		/**
		 * Reset the stream. If the stream has been marked, then attempt to reposition i at the mark. If the stream has
		 * not been marked, or more bytes than the readAheadLimit have been read, this method has no effect.
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void reset() throws IOException {
			synchronized (CircularByteBuffer.this) {
				if (inputStreamClosed) {
					throw new IOException("InputStream has been closed; cannot reset a closed InputStream.");
				}
				readPosition = markPosition;
			}
		}

		/**
		 * Skip bytes. This method will block until some bytes are available, an I/O error occurs, or the end of the
		 * stream is reached.
		 * @param n The number of bytes to skip
		 * @return The number of bytes actually skipped
		 * @throws IllegalArgumentException if n is negative.
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public long skip(long n) throws IOException, IllegalArgumentException {
			while (true) {
				synchronized (CircularByteBuffer.this) {
					if (inputStreamClosed) {
						throw new IOException(
							"InputStream has been closed; cannot skip bytes on a closed InputStream.");
					}
					int available = CircularByteBuffer.this.available();
					if (available > 0) {
						int length = Math.min((int) n, available);
						int firstLen = Math.min(length, buffer.length - readPosition);
						int secondLen = length - firstLen;
						if (secondLen > 0) {
							readPosition = secondLen;
						} else {
							readPosition += length;
						}
						if (readPosition == buffer.length) {
							readPosition = 0;
						}
						ensureMark();
						return length;
					} else if (outputStreamClosed) {
						return 0;
					}
				}
				try {
					Thread.sleep(100);
				} catch (Exception x) {
					throw new IOException("Blocking read operation interrupted.");
				}
			}
		}
	}

	/**
	 * Class for writing to a circular byte buffer. If the buffer is full, the writes will either block until there is
	 * some space available or throw an IOException based on the CircularByteBuffer's preference.
	 * @since ostermillerutils 1.00.00
	 */
	protected class CircularByteBufferOutputStream extends OutputStream {

		/**
		 * Close the stream, flushing it first. This will cause the InputStream associated with this circular buffer to
		 * read its last bytes once it empties the buffer. Once a stream has been closed, further write() or flush()
		 * invocations will cause an IOException to be thrown. Closing a previously-closed stream, however, has no
		 * effect.
		 * @throws IOException never.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void close() throws IOException {
			synchronized (CircularByteBuffer.this) {
				if (!outputStreamClosed) {
					flush();
				}
				outputStreamClosed = true;
			}
		}

		/**
		 * Flush the stream.
		 * @throws IOException if the stream is closed.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void flush() throws IOException {
			if (outputStreamClosed) {
				throw new IOException("OutputStream has been closed; cannot flush a closed OutputStream.");
			}
			if (inputStreamClosed) {
				throw new IOException("Buffer closed by inputStream; cannot flush.");
				// this method needs to do nothing
			}
		}

		/**
		 * Write an array of bytes. If the buffer allows blocking writes, this method will block until all the data has
		 * been written rather than throw an IOException.
		 * @param cbuf Array of bytes to be written
		 * @throws IOException if the stream is closed, or the write is interrupted.If buffer does not allow blocking
		 *         writes and the buffer is full. If the exception is thrown, no data will have been written since the
		 *         buffer was set to be non-blocking.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void write(byte[] cbuf) throws IOException {
			write(cbuf, 0, cbuf.length);
		}

		/**
		 * Write a portion of an array of bytes. If the buffer allows blocking writes, this method will block until all
		 * the data has been written rather than throw an IOException.
		 * @param cbuf Array of bytes
		 * @param off Offset from which to start writing bytes
		 * @param len - Number of bytes to write
		 * @throws IOException if the stream is closed, or the write is interrupted.If buffer does not allow blocking
		 *         writes and the buffer is full. If the exception is thrown, no data will have been written since the
		 *         buffer was set to be non-blocking.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void write(byte[] cbuf, int off, int len) throws IOException {
			while (len > 0) {
				synchronized (CircularByteBuffer.this) {
					if (outputStreamClosed) {
						throw new IOException("OutputStream has been closed; cannot write to a closed OutputStream.");
					}
					if (inputStreamClosed) {
						throw new IOException("Buffer closed by InputStream; cannot write to a closed buffer.");
					}
					int spaceLeft = spaceLeft();
					while (infinite && spaceLeft < len) {
						resize();
						spaceLeft = spaceLeft();
					}
					if (!blockingWrite && spaceLeft < len) {
						throw new IOException("CircularByteBuffer is full; cannot write " + len + " bytes");
					}
					int realLen = Math.min(len, spaceLeft);
					int firstLen = Math.min(realLen, buffer.length - writePosition);
					int secondLen = Math.min(realLen - firstLen, buffer.length - markPosition - 1);
					int written = firstLen + secondLen;
					if (firstLen > 0) {
						System.arraycopy(cbuf, off, buffer, writePosition, firstLen);
					}
					if (secondLen > 0) {
						System.arraycopy(cbuf, off + firstLen, buffer, 0, secondLen);
						writePosition = secondLen;
					} else {
						writePosition += written;
					}
					if (writePosition == buffer.length) {
						writePosition = 0;
					}
					off += written;
					len -= written;
				}
				if (len > 0) {
					try {
						Thread.sleep(100);
					} catch (Exception x) {
						throw new IOException("Waiting for available space in buffer interrupted.");
					}
				}
			}
		}

		/**
		 * Write a single byte. The byte to be written is contained in the 8 low-order bits of the given integer value;
		 * the 24 high-order bits are ignored. If the buffer allows blocking writes, this method will block until all
		 * the data has been written rather than throw an IOException.
		 * @param c number of bytes to be written
		 * @throws IOException if the stream is closed, or the write is interrupted.If buffer does not allow blocking
		 *         writes and the buffer is full.
		 * @since ostermillerutils 1.00.00
		 */
		@Override
		public void write(int c) throws IOException {
			boolean written = false;
			while (!written) {
				synchronized (CircularByteBuffer.this) {
					if (outputStreamClosed) {
						throw new IOException("OutputStream has been closed; cannot write to a closed OutputStream.");
					}
					if (inputStreamClosed) {
						throw new IOException("Buffer closed by InputStream; cannot write to a closed buffer.");
					}
					int spaceLeft = spaceLeft();
					while (infinite && spaceLeft < 1) {
						resize();
						spaceLeft = spaceLeft();
					}
					if (!blockingWrite && spaceLeft < 1) {
						throw new IOException("CircularByteBuffer is full; cannot write 1 byte");
					}
					if (spaceLeft > 0) {
						buffer[writePosition] = (byte) (c & 0xff);
						++writePosition;
						if (writePosition == buffer.length) {
							writePosition = 0;
						}
						written = true;
					}
				}
				if (!written) {
					try {
						Thread.sleep(100);
					} catch (Exception x) {
						throw new IOException("Waiting for available space in buffer interrupted.");
					}
				}
			}
		}
	}
}
